1. Field of the Invention
The present invention relates to a turbo machine having a rotor, surrounded by a housing, with a suction side and a pressure side, and having a shaft which is supported on both ends in a housing with suitable bearings and is sealed off with seals between the interior of the housing and the surroundings, and having an arrangement for absorbing the axial thrust generated by the pressure difference between the suction side and the pressure side.
2. Description of Background and Material Information
Turbo machines of the aforementioned type are known from numerous publications, such as Swiss Patent No. 663,447, dated Dec. 15, 1987, the disclosure of which is hereby expressly incorporated by reference in its entirety, and may for instance be embodied as turbo compressors of an axial, radial or combined type, or as turbo machines of some other kind, in which a pressure difference arises between the suction side and the pressure side of the rotor.
The pressure difference between the suction side and the pressure side of the rotor creates an axial thrust. In the most favorable case, this axial thrust can be absorbed by suitable axial thrust bearings. Although numerous embodiments of such bearings are known, their load capacities are limited, especially at high rpm and for significant pressure differences.
Attempts have therefore already been made to absorb the axial thrust, or at least reduce it, by means of special arrangements. Swiss Patent No. 449,659, dated Apr. 11, 1968, describes one such arrangement, in which the axial thrust is intercepted by a co-rotating pressure comb on a secondary shaft driven with gear-wheel transmission. This requires a complicated construction requiring a significant amount of space, however.
In other arrangements, the pressure difference on the pressure side is reduced by a pressure equalization piston with a labyrinth seal. This dictates major leakage losses, however, particularly in machines having a high pressure drop and a low pumping capability.
In modern turbo machines, which use especially low-loss bearings such as magnet bearings, these provisions are often inadequate, since axial thrusts can then be absorbed only to a very limited extent, because of the low thrust capacities. From U.S. Pat. No. 5,028,204, issued on Jul. 2, 1991, and European Published Patent Application No. 373,817, a turbo machine with a magnet-supported rotor is known in which seal gas is carried to the suction-side labyrinth seal, via a pipe that is flush with the shaft and is attached to the housing, and at the same time is carried to the end face of the shaft, at reduced pressure, via a dry gas seal. By throttling the outflow of seal gas, the force of the thrust on the end face can be adjusted and the axial thrust can be compensated for. Supporting the shaft on the suction side is impossible here, so that the turbo machine is embodied in an overhanging fashion. In heavy weight machines with a number of stages and a correspondingly long length, this feature is unusable, because of the lack of rotor stability. Furthermore, the labyrinth seal used does not allow a major pressure difference, or else causes undesired leakage losses.